Er... you'd collect PLEDGES. It's a tried and tested fundraising technique.
You could even have a little option where sponsors can opt to donate the pledged money even if you don't get on the pitch.
Or pay more if you win, get a the matchwinner etc.
Did you mean RAISES the most, Gareth? Given it's a charity match, I actually think that's a pretty reasonable criteria!
Maybe anyone who can't raise funds/doesn't have friends can be on the bench, or do the teamtalk or something?